Epidemiology Practice Questions

Q: In a study, 100 patients were telephoned and asked whether they exercise daily (exposure), and whether they have coronary artery disease now or ever before (outcome). Identify the study design.

Cross-sectional study. ***Cross-sectional study*** - This design measures **exposure** and **outcome** simultaneously at a single point in time, commonly referred to as a **prevalence study** or 'snapshot' study. - Because it assesses status at one moment, it cannot determine **temporality** or causality, making it ideal for determining disease prevalence rather than incidence. *Cohort study* - In a cohort study, researchers start with **exposure** status and follow participants over time to observe the development of an **outcome**. - It assesses incidence and is longitudinal, requiring a **follow-up period** which is absent in this scenario. *Case–control study* - This design involves identifying participants based on the presence of the **outcome** (cases) versus those without it (controls) and then looking back for past **exposures**. - Since the study described begins by asking about exercise habits without grouping participants by disease status first, it is not a retrospective case-control study. *Randomized controlled trial (RCT)* - An RCT is an **experimental study** where the investigator **actively intervenes** by randomly assigning patients to treatment or control groups. - This scenario is an **observational study** where the researcher only observes existing habits, rather than assigning exercise regimens.

Q: In a contraceptive study, 500 women were followed for 6 months. During this period, 4 pregnancies occurred. What is the Pearl Index?

1.6. ***1.6*** - The **Pearl Index** is calculated as (Number of accidental pregnancies × 1200) / Total months of exposure. - With 4 pregnancies over 3000 woman-months (500 women × 6 months), the calculation is (4 × 1200) / 3000 = 4800 / 3000 = **1.6**. *2.5* - This value is mathematically incorrect based on the standard formula for the **Pearl Index**. - It likely represents a calculation error where the numerator or denominator was inverted or miscalculated. *5.0* - This result would be reached if one incorrectly multiplied the pregnancies by 1200 and divided by 500 women without accounting for the **months of exposure**. - It fails to utilize the total **person-time of observation**, which is crucial for determining contraceptive failure rates. *2.0* - This would result from an incorrect assumption, such as calculating based on a shorter duration or misinterpreting the **total woman-months**. - It does not adhere to the validated epidemiological formula used to assess **contraceptive efficacy**.

Q: A health centre conducts screening of women in the community. An elderly woman is detected to have carcinoma of the cervix/breast during this screening. This activity corresponds to which level of prevention?

Secondary. ***Secondary*** - **Secondary prevention** involves **early detection** and **prompt treatment** of disease to stop its progression. - **Screening programs** like Pap smears for cervical cancer or mammography for breast cancer are classic examples of this level. *Primary* - **Primary prevention** includes measures applied *before* the disease occurs, such as **vaccination** or health education. - Its goal is to prevent the **onset of disease** rather than detecting an existing one. *Primordial* - **Primordial prevention** targets the underlying environmental and social conditions that lead to the causation of disease (e.g., **policies** promoting healthy diet or banning smoking). - It aims to prevent the emergence of **risk factor patterns** in the population rather than individual screening. *Tertiary* - **Tertiary prevention** applies when the disease is already established and symptomatic. - It focuses on **rehabilitation** and preventing **disability** or complications from the clinical disease.

Question 1

Define net reproduction rate

Accepted Answer

Total number of girl children born during the reproductive age of a woman taking into account mortality/Average no of female children a newborn girl will bear during her reproductive age assuming age specific fertility and mortality rates

Answer

Total number of children born during the reproductive age of a woman

Answer

Total number of girl children born during the reproductive age of a woman

Answer

Average number of live births per woman during her reproductive lifespan

Question 2

In a study, 100 patients were telephoned and asked whether they exercise daily (exposure), and whether they have coronary artery disease now or ever before (outcome). Identify the study design.

Accepted Answer

Cross-sectional study

Answer

Cohort study

Answer

Case–control study

Answer

Randomized controlled trial (RCT)

Question 3

In a contraceptive study, 500 women were followed for 6 months. During this period, 4 pregnancies occurred. What is the Pearl Index?

Accepted Answer

1.6

Answer

2.5

Answer

5.0

Answer

2.0

Question 4

A health centre conducts screening of women in the community. An elderly woman is detected to have carcinoma of the cervix/breast during this screening. This activity corresponds to which level of prevention?

Accepted Answer

Secondary

Answer

Primary

Answer

Primordial

Answer

Tertiary

Question 5

On evaluating an influenza vaccine, it demonstrated an efficacy of 95% in randomized controlled
trials and an effectiveness of 90% in post-marketing surveillance studies. Which of the following
statement is incorrect?

Accepted Answer

The vaccine confers absolute and complete protection against influenza infection

Answer

Vaccinated individuals demonstrate a 95% reduction in disease risk vs unvaccinated

Answer

Vaccinated individuals show a 90% reduction in influenza risk in real-world settings

Answer

Vaccine effectiveness can be lower than efficacy in real-world settings

Epidemiology — MCQs

Epidemiology — MCQs

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